Magnetron discharge tube circuit



Patented Oct. 1, 1940 UNITED STATES MAGNTRON DISCHARGE TUBE CIRCUIT Waldemar Ilberg, Berlin,

Germany, assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application December 16, 1937, Serial No. 180,103 In Germany December 30, 1936 3 Claims.

This invention relates to circuits for the stabilization of the discharge action in magnetron tubes. There is an annoying effect frequently met with in the operation of magnetron trans- 5 mitters, that when, for instance, the load changes or when unusually high modulation peaks occur, the oscillations become interrupted and must be restored by artificial means either through temporary adjustment of the magnetic field or through change of the operating potentials. In this specication a circuit principle is disclosed which overcomes the aforementioned undesirable effect and assures operating stability of the magnetron discharge tube. In addition, and as a result of circuits based on this invention, it is possible to obtainqa better linear modulation characteristic giving a straight line over a wider range.

One method aiming at the stabilization of 'mag- N netron generators is set forth in German Patent 476,404 (issued May 16, 1929) which shows additional windings alongside the main magnet winding. The additional windings may be energized by the total emission current...l The resulting magnetic field has its intensity regulated to maintain the negative resistance of the discharge path and thereby the frequency of the generated oscillations at a constant value.A Such circuits do not admit a high` degree of modulation, and be- 0 sides are practically dependent upon an electrically excited main magnetic field.

This invention deals with circuits which may be used, if desired, for frequency modulation. The magnetron tube can be worked, if need be,

with a permanent magnet whose ileld intensity is not easily varied by electrical means. Nor is it necessary to use all of the discharge current for stabilization inasmuch as the current of a portion of the discharge path is suihcient.

40 The distinguishing feature of the circuit based on this invention is that the current of a portion of -the discharge path is caused to act preferably on the bias potentials of the electrodes in such a manner as to avoid an interruption of oscillations and thus to give a betterl modulation characteristic.

For the carrying out of this idea magnetron tubes are used with several positively biased electrodes and the partial discharge current from one electrode is put through a resistance to obtain a voltage drop. These resistances should be predominantly of ohm'ic nature while their shape or form is immaterial. They may be independent of temperature variations if required or else may have compensating positive and negative temperature coeflicients. If it is required that these resistances respond very quickly to any change of current or potential, 'it is preferable to use glow tubes yas negative resistances. 'I'he potentials appearing across-the resistance will be addi- 5 tive to or subtractive from the biasing potential' of the same electrode or that of another electrode group.

My invention will now be explained in more detail by reference to the accompanying drawing, l0

in which: y

Figurel shows diagrammatically a novel circuit arrangement for a magnetron discharge tube as used in my invention;

Fig. 2 shows a modification of both the circuit 15 and the magnetron tube, the latter being provided with auxiliary electrodes; and

Fig. Bshows still another modification of the circuit arrangement.

In Fig. 1 is illustrated a split anode magnetron 20 tube in cross section. The anodes Ai and Az are connected across an oscillating circuit C, L and L". At the point of junction of the two inductances L' and L is inserted a condenser 3, the capacitance of which acts as a short circuit 25 for high frequencies and at the same'time serves the purpose ofblocking the different direct cur rent plate potentials.

From one side of the condenser 3 there is a direct lead to the positive terminal of the anode 30 potential source k4. From the opposite side of this condenser is connected a resistance 5 leading to said potential source. 'I'he negative terminal of the direct current source 4 is connected to the cathode K. The discharge spaceis con- 35 tained in an envelope R. A source of modulating potentials M is preferably coupled through a transformer 6' to the circuit leading from the source l to the two anodes Ai and A2 by way of the inductances L' and L'f respectively. 40 In Fig. 2 a magnetron is shown with a one piece anode 1 and `auxiliary electrodes B and 9.

' Corresponding elements of this circuit and of the circuit of Fig. lare given like references. In the anode power lead is inserted an ohmic resistance 45 5 which, if necessary, can be shunted by the condenser |0 which does not offer any appreciable resistance to either the modulation or the high frequencies. The leads of the two auxiliary electrodes 8 and 9 are connected across the resist- 50 ance' 5. -An axially directed electrostatic field which is set up between the auxiliary electrodes 8-9 and the cathode K varies according to the magnitude of the anode current. In this variable crosseld the electron paths are somewhat deilected. Thus the electron paths are not perpendicular to the cathode but are more or less spiraled with their axis inclined towards the cathode. 'I'he'result thereof is that a break in the oscillations is avoided.

Fig. 3 shows a cross sectional view of a magnetron tube having an outer screen ior protective electrode N and a plurality oi inner anodes Ar and A2. Under normal conditions the outer electrode N is at highest positive potential with respect to cathode K. Under these assumptions one side of the bias voltage source 4 is common to all electrodes. The anode current is fed from source 4 through a resistance I2 having a negative temperature, coemcient. This resistance, therefore, becomes lower when the total anode current increases. The external electrode N is positively biased withrespect to the direct current potential applied to the anodes iii-A2, the increased potential being supplied by a battery or other source I3. Materials such as Urandioxide and Thyrite can be employed in making resistors with a negative temperature coeicient. Such resistors resemble porcelain and consistl of admixtures of conductive and non-conductive particles, where the latter predominates.

The basic idea of the invention is not limited to the herein illustrated and described examples. Its realization can be carried out in a variety of ways. For instance, especially in the case of electrically excited magnetic iields a portion of the anode current can be used in an amplifying sense by means of a supplemental winding in the magnetic eld exciting system. Normally, then, the operating points are so chosen, that only a part of the electron stream reaches the anode, the remaining electrons being spiraled by the delecting magnetic field. In the event that the anode voltage should be lowered, under the known normal operating conditions there would be a danger of interruption of the oscillations because of the insuiiicient number of electrons reachingthe anode. In a circuit arrangement of my invention a reduction of anode current is necessarily laccompanied by a reduction in the resultasians ing magnetic field. There will be less spiraling of electron paths and a condition similar to the normal will continue to prevail. It is to be understood that the idea of the invention is not limited to transmitters but can be applied also to receivers, especially of the heterodyne type.

I claim: l I

1. A circuit arrangement including an electron discharge tube having, a cylindrical anode, a linear cathode within the anode, end-plates adjacent the extremities of the anode, and magnetic field exciting means for controlling the emission paths in said tube, sources of operating potentials applied between the cathode and anode, lsaid sources including direct current potentials and modulating potentials, a connection having negligible resistance from the positive side of the direct current source to one of said end-plates and a circuit including a predominantly ohmic resistor connected from said direct current source to the other of said end-plates, and to said anode, said resistor constituting self-biasing means applicable to one of said end plates and operable in dependence upon its own conductance fo insuring stable operation of said tube.

2. A circuit arrangement according to claim i wherein said resistor possesses a negative temperature coeicient.

3. In a circuit arrangement comprising an elec tron discharge tube having a cathode, a cylindrical anode surrounding the cathode, and a plurality of end plate electrodes, a magnetic field exciting means for controlling the lcourse of electrons in the discharge space between the cathode and the anode, means including a resistor for applying unlike direct current potentials to different ones of said end plate electrodes, and a modulating source connected in circuit between said cathode, said direct current source, said resistor and said anode; said modulating source being operative to render saidresis'tor effective to vary the potential diierence between said end plate electrodes.

WALDEMAR. ILBERG. 

